In many projection units which include a preformed glass reflector and projection lamp capsule (e.g., tungsten halogen) therein, the lamp capsule is retained in alignment with the reflector by employing a suitable cement (e.g., sauereisen) within the reflector and about the lamp's sealed end. Examples of such arrangements are shown in U.S. Pat. Nos. 3,314,331 (Wiley) and 3,639,750 (Anthonijsz). Use of cement or a similar permanent-type bonding agent prohibits separation of the lamp capsule and reflector in the event that replacement of either of these components is necessary. In almost all cases, it is only the incandescent lamp capsule which fails and needs replacement. The aforementioned permanent bond between lamp and glass reflector was believed essential to assure precise alignment between said components and between these members and other elements (e.g., film gate, projection lens) within the overall system. Alignment between the reflector and lamp was usually achieved using a precisioned instrument whereupon the assembled unit was ready for insertion within a respective socket holder arrangement, such as shown in U.S. Pat. No. 3,789,212 (Wagner). This latter positioning is usually accomplished by the projector's operator.
Mandatory replacement of both lamp and glass reflector has therefore resulted in unnecessary waste of material which in turn has added appreciably to the overall cost of operating such systems.
The projection unit of U.S. Pat. No. 4,156,901 (Haraden et al) was designed to eliminate the above undesired requirement by providing a retention member which is removable from within the reflector yet which also assures positive alignment of the unit's incandescent lamp with the reflector when said lamp is positioned therein. The retention member is secured to the lamp's sealed end and comprises a metallic "can", a preformed component of insulative material such as ceramic, or a combination of both. One particular disadvantage with the unit of U.S. Pat. No. 4,156,901 was the requirement for providing grooves, slots, etc. within the reflector's elongated neck portion to accommodate the retention member, which in turn included protruding tabs or similar items for being finally positioned within these grroves. Yet another disadvantage of the unit of U.S. Pat. No. 4,156,901 was that the reflector opening to accommodate the unit's retention member had to be relatively large, thus reducing the available reflective surface area of the reflector.
The projection unit described in U.S. Pat. No. 4,219,870 (Haraden et al) was designed as an improvement over the afore-described unit of U.S. Pat. No. 4,156,901 by providing means whereby the retention member having the sealed end of the lamp therein may be removed from the front, concave reflecting portion of the glass reflector. The method of removal for these components in U.S. Pat. No. 4,156,901 was through the rear (neck) opening of the reflector. Rearward removal proved difficult in the complete system due to the typically limited accessibility in this region of the system. In U.S. Pat. No. 4,219,870, the resulting unit also required a metallic "can" on the end of the lamp capsule, as well as the aforementioned grooves, slots, etc. within the opening in the reflector's neck. This opening was substantially smaller, however, than that in U.S. Pat. No. 4,156,901 but in order to accomplish this it was necessary to provide a second, external springlike retention member as well as grooves in the neck's external surface to accommodate this second member.
In addition to the above, several versions of various front-loading projection units are described in Ser. No. 212,398, Ser. No. 212,469, and Ser. No. 212,470, all of which are assigned to the same assignee as the instant invention. All of these units require provision of slots or grooves within the glass reflector's neck portion in order to effect proper alignment of the lamp capsule therein. In addition, all require utilization of a metallic "can" or similar component secured to the end of the capsule (about the sealed end of the lamp itself) which must be inserted within the reflector's neck. As also in the case of the above units, this "can" member includes protuberances or similar projecting portions in order to align the capsule, said protuberances being slidably positioned within the corresponding grooves or slots of the reflector. Still further, the above units require some additional means of accomplishing capsule securement, such as a threaded nut, wireform, or locking cantilever spring member.
Yet another embodiment of a projection unit having a separable lamp capsule is described in Ser. No. 217,627, which is also assigned to the same assignee as this instant invention. In this unit, the capsule also includes an attached metallic "can" in addition to a pair of projecting flanges which slidably engage both the neck of the reflector and upstanding rear part of the unit's metallic U-shaped holder. Once the capsule was inserted, it is necessary in Ser. No. 217,627 to thereafter attach the preferred socket component, which itself constitutes a separate part of the system. It is thus necessary in this unit to precisely locate the flange portions relative to the capsule's filament structure in order to provide proper flament orientation within the reflecting region of the reflector. Such a procedure is understandably both costly and time-consuming.
It is believed, therefore, that a projection unit which provides for facile separation of the lamp component from within the unit's reflector and/or socket member without the foregoing disadvantages of the units such as described above would constitute a significant advancement in the art.